Background: Radiotherapy for retroperitoneal sarcomas remains controversial and a technical challenge considering the threshold of contiguous critical organs tolerance. We performed consecutive RapidArc dosimetric plans in preoperative or postoperative setting.
Methods: A dosimetric study was carried out from six preoperative (group A) and four postoperative (group B) CT-scans, performed in 7 patients.Prescribed dose was 45 and 50 Gy for groups A and B, respectively. The planning target volume (PTV) was defined as the clinical target volume (CTV) plus 5 mm. The CTV encompassed the gross tumor volume (GTV) plus 10 mm or the tumoral bed. The dosimetric plans were optimized on a RapidArc Eclipse console using the progressive resolution algorithm, PRO version 8.8. Normalization method allowed the coverage of 99% of the PTV by 95% of the dose.
Results: Mean PTV were 2318.5 ± 2223.9 cc [range 348-6198 cc] and 698.3 ± 216.6 cc [range 463 -933 cc] for groups A and B, respectively. Plans were optimized for single arcs in group B and for single or two arcs in group A. The contralateral kidney volume receiving 5 Gy (V5Gy) was 21.5 ± 23.3% [range 0-55%] and 3.1 ± 2.6% [range 0-7.3%] for groups A and B, respectively. The mean dose received by 1% of the kidney (D1%) was 5.6 ± 2.4 Gy [range 3.6 -7.6 Gy] for group A and 5.4 ± 0.7 Gy [range 4.3-6 Gy] for group B. The volume of small bowel excluding the PTV (small bowel-PTV) that received 40 Gy and 30 Gy (V40Gy and V30Gy) in group A were 7.5 ± 4.4% [range 5.4-14.1%] and 18.5 ± 7.1% [range 10-30.4%], respectively.In group B, small bowel-PTV V40Gy and V30Gy were 4.7 ± 3.3% [range 3.3-8%] and 21.6 ± 7.5% [range 9.4-30%] respectively. In a second step, we treated two patients in the postoperative group. Treatment time delivery with one arc was 74 seconds. No severe acute toxicity was observed.
Conclusion: RapidArc technology for retroperitoneal sarcomas showed acceptable dosimetric results in preoperative or postoperative clinical situation. From the first treated patients, acute tolerability was good to excellent.